No abstract

Land-use intensification is a central element in proposed strategies to address global food security. One rationale for accepting the negative consequences of land-use intensification for farmland biodiversity is that it could ‘spare’ further expansion of agriculture into remaining natural habitats. However, in many regions of the world the only natural habitats that can be spared are fragments within landscapes dominated by agriculture. Therefore, land-sparing arguments hinge on land-use intensification having low spillover effects into adjacent protected areas, otherwise net conservation gains will diminish with increasing intensification. We test, for the first time, whether the degree of spillover from farmland into adjacent natural habitats scales in magnitude with increasing land-use intensity. We identified a continuous land-use intensity gradient across pastoral farming systems in New Zealand (based on 13 components of farmer input and soil biogeochemistry variables), and measured cumulative off-site spillover effects of fertilisers and livestock on soil biogeochemistry in 21 adjacent forest remnants. Ten of 11 measured soil properties differed significantly between remnants and intact-forest reference sites, for both fenced and unfenced remnants, at both edge and interior. For seven variables, the magnitude of effects scaled significantly with magnitude of surrounding land-use intensity, through complex interactions with fencing and edge effects. In particular, total C, total N, δ15N, total P and heavy-metal contaminants of phosphate fertilizers (Cd and U) increased significantly within remnants in response to increasing land-use intensity, and these effects were exacerbated in unfenced relative to fenced remnants. This suggests movement of livestock into surrounding natural habitats is a significant component of agricultural spillover, but pervasive changes in soil biogeochemistry still occur through nutrient spillover channels alone, even in fenced remnants set aside for conservation. These results have important implications for the viability of land-sparing as a strategy for balancing landscape-level conservation and production goals in agricultural landscapes.

The way in which species interactions are altered at habitat edges is an emerging concern in conservation biology, with some theories predicting edge‐affected habitats to be less stable and exhibit intensified species interactions relative to interior habitats. One little‐studied interaction is phoresy, where an individual of one species attaches itself to an individual of another species for the purpose of dispersal. Bumble bees (Bombus spp.) are important crop pollinators around the world and at least 10 species of phoretic mites have been associated with various bumble bee species. Here, we investigated changes in the abundance of the introduced European B. terrestris across forest‐grassland edges in the Southern Alps of New Zealand, and concomitant changes in the phoretic mite loads on these mobile pollinators. Bumble bees penetrated up to 250 m inside forest fragments, with abundance declining with distance from the anthropogenic matrix habitat. By contrast, phoretic mite loads increased towards the forest interior. Overall, phoretic mite loads on B. terrestris were greatest in the forest canopy, suggesting that this species interaction is intensified in natural habitat compared to that in the anthropogenic land use surrounding forest fragments. Our data indicate that phoretic loads on bumble bees are elevated in forest canopies. The functional significance of altered bumble bee – mite interactions for pollination services at forest edges remains to be tested.

Mesopredator and competitor release can lead to population increases of invasive house mice (Mus musculus) after larger introduced mammals are controlled or eradicated. In New Zealand, mammal-resistant fences have enabled multi-species mammal eradications in order to protect indigenous species. When house mice are the only mammals remaining in these biodiversity sanctuaries, they may reach a high population density, with potential consequences for their indigenous prey. We studied mouse populations in the absence of other mammals for 5 years at mammal-resistant fenced forest sites at Maungatautari, Waikato. We used spatially explicit capture-recapture (SECR) to estimate mouse population density quarterly in two independently fenced sites, with contrasting levels of mouse management that were switched half-way through the study. In the absence of mouse control, mouse population density reached 30-46 ha -1 at one site each year after summer breeding, and 23 ha -1 at the other site. Mouse tracking rates in inked footprint tunnels were positively related to numbers of mice captured in each session, but not significantly to mouse density. The highest mouse densities were similar to estimates in New Zealand forest and alpine ecosystems after mass seeding (masting) events, but lower than estimates in another sanctuary and on some islands lacking larger terrestrial mammals. We suggest that in the absence of competition and predation from other mammals, food limitation may have prevented mouse populations from attaining very high densities in this mainland forest location.

Aims: Aerially applied glyphosate is an economic tool to deal with large areas of invasive plants. However, there are few studies investigating non-target effects or rates of reinvasion, particularly over multi-year time frames. The aims were to evaluate the effectiveness of aerial application of glyphosate for control of dense stands of the invasive grey willow Salix cinerea, and determine the vegetation trajectory over the subsequent 2 yr.Location: Whangamarino Wetland, Waikato, New Zealand.Methods: A before-after control-impact (BACI) experiment was conducted in a Ramsar-listed wetland in New Zealand. Effects on S. cinerea cover, canopy light interception and non-target damage were monitored over a 7.1 ha experimental area prior to, and for 2 yr following, aerial application of glyphosate. Vegetation classification, ordination and species richness analyses were undertaken to describe community-level effects.Results: Aerial application of glyphosate to an established willow canopy was effective in reducing cover to <5% on average for up to 2 yr post-spray when assessed using 100 m 2 vegetation survey plots. Smaller 1 m 2 plots were more sensitive for detecting willow reinvasion, which was noted from 1 yr post-spray. Collateral damage to non-target sub-canopy species was generally minimal, except for the native tree fern Dicksonia squarrosa, which showed marked reductions in cover and no recovery over the study period. Species richness was higher in sprayed plots post-spray and a shift towards a native Carex-dominated sedgeland community was detected.Conclusions: Aerial application of glyphosate to a dense canopy of mature willow was effective in reducing the cover and dominance of this invasive wetland tree species. Minimal collateral damage occurred, facilitating recovery and expansion of a native sedgeland community. The risk of secondary invasion did not eventuate, although exotic species richness spiked in the year following spraying. Sedgelands are susceptible to willow reinvasion via seed, so longerterm trajectories will diverge depending on management intensity. Using currently available tools, the management options are either repeated cycles of herbicide application to redirect the trajectory from reinvasion to short-statured sedgelands, or intensive initial management to establish an alternative, more resilient trajectory to native wetland forest.